1. Field of the Invention
The present invention relates to an image display device and a control method thereof.
2. Description of the Related Art
Among image display devices, there are types that include a liquid crystal panel with a color filter, and a light source device (backlight device) that emits white light to the rear surface of the liquid crystal panel.
A backlight device has a problem in that the brightness from the light source changes. Change in the brightness is caused by, for example, changes in the emission characteristics of the light source due to changes in the temperature, aging deterioration of the light source, among other reasons. With a light-emitting device including a plurality of light sources, brightness variation (brightness unevenness) of the plurality of light sources will arise due to variations in the temperature and aging deterioration level of the plurality of light sources.
As a method of alleviating the foregoing brightness change or brightness unevenness, known is a method of measuring the brightness of the light source using an optical sensor, and adjusting the amount of luminescence of the light source based on feedback. Specifically, known is a method of providing an optical sensor that detects, of the light emitted from the backlight device, reflected light that is reflected off an optical sheet (optical member) of the backlight device and returns to the light source side, and adjusting the amount of luminescence (light emission control value) of the light source based on the detection value of the optical sensor. This type of technique is disclosed, for example, in Japanese Patent Application Publication No. 2011-27941.
As an optical image that is used in an image display device, known is an external light sensor that detects the user's environmental light (external light of lamps or the like). As an external light sensor, there is a type that is disposed on a frame (bezel part) of the display screen, and detects the luminance and color of the external light. Japanese Patent No. 4875590 discloses an example of this type of external light sensor.